During the Devonian Period, lungfishes underwent rapid diversification. Such rapid diversification has marred phylogenetic analyses and is suspected as being responsible for reducing phylogenetic hypotheses to large polytomies. This problem is exacerbated by poor morphological understanding of key Devonian taxa comprising loosely defined, paraphyletic lungfish families. Pentlandia macroptera Traquair, 1888, is one such taxon that has not received a detailed assessment since it was first discovered nearly 130 years ago. A detailed redescription of P. macroptera demonstrates that it resides in the monophyletic crown group of Devonian lungfish comprising phaneropleurids, fleurantiids, and scaumenacids but, at this stage, establishment of a new family based on this clade is not warranted. It is considered to be the most derived Middle Devonian lungfish. Several previously unrecognized structures for this taxon are described including the circumorbital bones, the cheek bones, cranial ribs, the lower jaw, and tooth plates, all of which show the derived condition. Pentlandia macroptera is also considered derived in possessing an unossified snout and neurocranium and represents the first occurrence of these conditions that were later to become prevalent in Carboniferous dipnoans. Of greatest significance, P. macroptera demonstrates the presence of the oldest pelvic girdle seen in the Dipnoi, which is conserved in form through to the Upper Devonian and even modern lungfish. The current work indicates that many of the derived characteristics of Late Devonian and Carboniferous dipnoans had their origin in the Middle Devonian.